Rapid method for the isolation of petrolenes from asphalt



United Sta- 6. Patent RAPID METHOD FOR THE ISOLATION OF PETRO- LENES FROM ASPHALT No Drawing. Application August 28, 1956 Serial N0. 606,579

2 Claims. 01. 208 -337) This invention relates to a method for rapidly iso lating petrolenes from asphalt and, more particularly, to an improved method for the substantially complete removal of pentane from the petrolene solutions obtained by extraction of asphalt with pentane.

i Petrolenes are one of the two principal components of asphalt, the other component being asphaltenes. The term asphalt as used herein applies to both native asphalts and pyrogenous asphalts. Native asphalts include asphalts occurring naturally in a pure or fairly pure state, and asphalts associated naturally with a substantialproportion of mineral matter such as sand, sandstone, clay, etc., which can be separated from the asphalt by solvent extraction methods. Pyrogenous asphalts include residues obtained from petroleum by various means, such as by distillation (e.g. still bottoms or residual oil) by blowing (e.g. blown asphalts), etc. Asphalts are considered to be colloidal systems in which asphaltenes constitute the dispersed phase and petrolenes the dispersing phase. The petrolenes are defined as that portion of the asphalt which is soluble in 50 volumes of the crude asphalt is reduced until the desired petrolene viscosity is attained. The residuum may then be oxidized to convert the petrolenes to asphaltenes until the product has the proper penetration, without appreciably changing the petrolene viscosity.

Utilization of this method of control of the asphalt as set forth in the Hardman patent means as a practical matter that the petrolene viscosity must be susceptible of rapid and easy determination. Unfortunately, the techniques ordinarily employed to ascertain petrolene viscosity require at least 4 hours for each determination. Two principal operations are required in this determina tion, first, the separation and recovery of the petrolenes from the asphalt by extraction with 50 volumes of pentane per volume of asphalt and followed by removal of the pentane and, second, the determination by physical measurements of the petrolene viscosity and density. The separation and recovery of the petrolenes requires about 1% to 2 hours, and the physical measurements require about 2% hours. The removal of the pentane is the most time-consuming portion of the first operation. At the present time, under the standard method STM 126 the bulk of the pentane is removed from the petrolene pentane solution by simple distillations, and traces of pentane are removed by steam-stripping.

The petrolene viscosity is exceedingly sensitive to small amounts of pentane. As little as 0.25% pentane can lower the viscosity of the petrolenes from 15,000 to 5,000 poises. Since the determination must be reproducible within 250 poises, substantially complete removal of the pentane obviously is required. To achieve normal pentane per volume of asphalt. The asphaltenes are defined as that portion which is soluble in carbon disulphide and insoluble in 50 volumes of normal pentane per volume of asphalt.

It is now known that asphalt may be considered as a four-variable system whose properties are governed by the values of the penetration, weight percent of asphaltenes, petrolene viscosity and petrolene viscosity gravity constant. Harley F. Hardman, in his Patent vNo. 2,738,312, issued March 13, 1956, has shown how' to control the nature of the asphalt used for paving purposes so as to produce a uniform product of long service life. It is apparent that arbitrary choice of any three of the four variables of the asphalt system means'that the fourth variable is controlled by the correlation. Moreover, asphalt is characterized commercially by the viscosity gravity content of the refined asphalt, which value is predetermined by the selection of the crude stock from which the asphalt product is obtained. Thus, this variable of the four-variable system is predetermined at the outset of each refining operation.

The penetration variable in the four-variable system is set by the specifications required for the specific asphalt being prepared. The penetration or consistency of the asphalt is the most commonly specified property of asphaltic materials, and is governed by the use to 'which the asphalt is to be applied- It is a specified value which the asphalt must meet to be satisfactory for' the intended use. Thus, the variable of penetration value also is predetermined.

The remaining variable which Hardman suggests should be elected by the refiner to fix arbitrarily is the petrolene viscosity, because of the ease of operating and controlling a distillation apparatus, as compared to an asphalt oxidizer. presupposes that the petrolene viscosity is known, and on the basis of this knowledge a substantially complete removal rapidly has proved surprisingly difiicult.

In one attempt to reduce the time required for removal of the pentane, the pentane solution was flowed in a thin film down the wall of a vertical steam-jacketed column, the interior of which was held under a moderate vacuum or swept of vapors by a gas stream. The par tialiy stripped petrolene solution was then conducted through a second stage column maintained at less than 1 mm. absolute pressure where it was allowed to flow in a thin film over an electrically heated surface. At the slowest practical flow rate, and a surface temperature of 450 F., the following comparison of petrolene viscosities with the standard procedure was obtained.

Petrolene Method Vis STM 126.

Two-stage vacuum column poises.

poises.

' 1 Average of 7 determinations.

' with a second stage evaporation by directing a stream of inert gas across'the surface of the solution. By this method, the time required for separation and recovery of petrolenes from vthepentane solution is about 1 hour, as compared with 1% to 2 hours for STM 126 (the standard method). As a further feature of the in'ven tion, the petrolenes are initially separated from the asphalt by refluxing the asphalt sample with the pentane. Unless refluxing is used, there is a significant decrease in theaverage petrolene viscosity obtained, apparently because of incomplete solution of the heavier petrolene fractions in the pentane.

The following procedure is recommended for the isolation of the petrolenes from the asphalt:

A standardized amount of hot asphalt is weighed into a suitable flask; as an example, 8 g. of the hot asphalt can be weighed into a 1 liter flask. The asphalt is spread in a thin layer over the bottom of the flask by heating it on an electric hot plate. 50 volumes of n-pentane then are added. Thus, in the case of 8 g. of asphalt 400. ml. of pentane would be added. The flask is then placed under reflux, and refluxing continued for 10 minutes, at the end of which time the flask is allowed to cool. The solution is filtered, and then prepared for removal of a major proportion of the pentane by flowing it in a thin film over a heated surface, for example, the inner surface of a jacketed steamheated condenser or electrically-heated surface, which thus functions as a steam stripper. This operation is carried out under a vacuum of about 375 mm. or less, thus materially assisting removal of the pentane.

The temperature of the surface over which the pentane solution is flowed will be within the range from about 200 to about 600 F. It is desirable to flow the pentane solution over the surface at such a rate that visible pentane evaporation occurs only on the upper portion of the surface. When the entire solution has passed over the surface the vacuum is disconnected, and the solution then conducted to the gas evaporation bath for removal of residual pentane.

The latter consists of an insulated solid metal block provided with a thermometer well and with beaker wells and gas jets with removable adapters for the beakers placed in the wells. The metal block is electrically heated, capable of being thermostatically controlled between 250 and 600 F. The .bath is brought to the desired temperature and the gas flow adjusted to maintain a flow of dry gas. The .beakers containing the solution to be stripped are placed in the block, preheated for Extraction.--Weigh approximately 8 g. of the hot asphalt into a 1 liter flask. Spread the asphalt in a thin layer over the bottom of the flask by heating on an electric hot plate.

Add 400 ml. of n-pentane.

Place the flask in a heater, attach a condenser and reflux the pentane for 10 minutes. Circulate cold water through the condenser. Use a low heat and do not allow the pentane vapors to rise above the second ball in the condenser. A boiling chip (Fisher 9-19l10) placed in the flask will prevent bumping.

At the end of the reflux period, remove the heater and allow the flask to cool until boiling subsides.

Filtering and removal of pentane.Apply vacuum. With steam passing through the condenser jacket, pour the pentane solution into the filter paper placed in the funnel at such a rate that visible pentane evaporation occurs only in the upper half of the condenser.- When the entire solution has passed through the evaporator, disconnect the vacuum.

Steam stripping-Steam-strip the remaining pentane in the steam evaporation bath. With the bath at operating temperature of 500 F., open the main steam valve and regulate the flow with the needle valve in the line to the block to maintain the required pressure for the specified steam flow.

Initially, have the removable adapters in place and dummy beakers in the wells to catch any trapped water which may be expelled from the steam line at start up. Regulate the water draw-off valve to the minimum opening required to maintain a flow of dry steam.

Remove the adapters and the dummy beakers. Drop the beakers containing the concentrated petrolene solution into the block and preheat for one minute. Attach the adapters and steam-strip the sample for 25 minutes at a rate of 40.3 mols steam/minute. Shut ofl the steam valve and remove the adapters and beakers.

Extensive comparisons have been made of the petrolene viscosity values obtained using this procedure for the separation of pentane with the standard method STM 126. Data typical of that which has been obtained is given in the following table for a series of different asphalts.

Comparison of STM and revised method on several asphalts Vis. 100 F. Poises Density 100 F. 100 F., V. G. C. Asphalt Type Pen.

STM Revised Difi. STM Revised Diff. STM Revised Diff. Method Method Method Illinois-Oklahoma 181 1, 185 1, 253 +68 0. 958 0. 957 O. 001 0. 818 0. 809 0. 009 Illinois-Oklahoma 298 757 822 +65 0. 956 0. 952 -0. 004 0. 841 0. 830 0. 011 MississipprArkansas. 70/80 273 288 +15 0. 949 0. 950 +0. 001 0. 8 18 0. 853 +0. 005 West Texas oxidized 96 310 242 68 0. 930 0. 927 0. 003 0. 805 0. 811 +0. 006 Illinois-Oklahoma blend 85/100 812 759 53 0. 957 0. 956 0. 001 0. 842 0. 841 0. 001

1 minute, attached to the gas line and the solution stripped for the required time by conducting a flow of dry gas into the beaker. Any inert gas can be used, for example, dry steam, nitrogen, helium, argon, carbon dioxide, methane, and flue gas (mixture of C0, C0 H O, N and CH Gas stripping is continued until pentane no longer is detected in the eflluent stream. This usually requires about 25 minutes, under the conditions stated. The petrolenes then can be removed and are ready for determination of petrolene viscosity by standard methods.

The following is an example which in the opinion of the inventors represents the best embodiment of their invention for the isolation of petrolenes:

EXAMPLE Thedata shows that the method of the invention does not give a petrolene viscosity which is substantially different from that obtained by the standard method. However, the method of the invention can be carried out in 1 hour, whereas the standard method requires 1% to 2 hours. The rapidity of separation of the pentanes substantially completely thus is remarkable.

We claim:

1. A process for the isolation of petrolenes from asphalt for the determination of petrolene viscosity which comprises mixing the asphalt with a sufiicient amount of n-pentane to dissolve substantially all of the petrolenes in the asphalt, refluxing the asphalt with the n-pentane for a time sufiicient to eflect complete solution of the petrolenes, flowing the petrolene-pentane solution in a thin film over a surface heated to from v200 to 600 F. at a slow rate under a vacuum of at least 375 mm. to

efiect removal of the bulk of the pentane and directing a. flow of inert gas at a temperature within the range from about 250 to about 600 F. across the surface of the residual petrolene pentane solution to effect substantially complete removal of the residual pentane.

2. A process in accordance with claim 1 in which the inert gas is dry steam.

References Cited in the file of this patent UNITED STATES PATENTS Davey Ian. 12, 1943 Sorem Jan. 2, 1945 Hardman Mar. 13, 1956 Agoston Feb. 26, 1957 

1. A PROCESS FOR THE ISOLATION OF PETROLENES FROM ASPHALT FOR THE DETERMINATION OF PETROLENE VISCOSITY WHICH COMPRISES MIXING THE ASPHALT WITH A SUFFICIENT AMOUNT OF N-PENTANE TO DISSOLVE SUBSTANTIALLY ALL OF THE PETROLENES IN THE ASPHALT, REFLUXING THE ASPHALT WITH THE N-PENTANE FOR A TIME SUFFICIENT TO EFFECT COMPLETE SOLUTION OF THE PETROLENES, FLOWING THE PETROLENE-PENTANE SOLUTION IN A THIN FILM OVER A SURFACE HEATED TO FROM 200 TO 600*F. AT A SLOW RATE UNDER A VACUUM OF AT LEAST 375 MM. TO EFFECT REMOVAL OF THE BULK OF THE PENTANE AND DIRECTING A FLOW OF INERT GAS AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 250 TO ABOUT 600*F. ACROSS THE SURFACE OF THE RESIDUAL PETROLENE PENTANE SOLUTION TO EFFECT SUBSTANTIALLY COMPLETE REMOVAL OF THE RESIDUAL PENTANE. 